Firescale prevention

I use a mixture of denatured alcohol and boric acid powder to prevent firescale. When I have to heat the silver more than once, do I have to paint it with the mixture each time or does one painting of it do?


Emily…Are you replying to another discussion or starting your own?..Rob

Hi Emily,

as the barrier flux “works”, it absorbs copper oxides, and as a result starts to turn blue as it gets saturated…and when it is really saturated it doesn’t work as well, so i would use that as an indication for when it is time to pickle clean and re-apply

i usually flow a set of solder jounts, pickle, then set up more sets if necessary

(my non-technical understanding/ explanation​:rofl::joy:…i am sire others can explain more accurately)


Hi Rob,
I didn’t find the answer in the discussion notes so asked my own question. Is that starting a new discussion?


When I use the combo of Boric acid and alcohol before annealling, for example, and then do some work on the piece of silver and then put it
in the pickle, and then if I need to use the torch again to solder something on it, do I have to reapply the boric acid mix to prevent firescale?


Hi Emily,
yes, re-apply the flux before heating again.
the pickle will have disolved the flux off the piece.

i forgot to mention that another purpose for flux is to create a barrier on the surface of the metal, absorbing the oxygen from the torch, thereby helping to prevent it from combining with the copper in the sterling silver alloy, and creating cupric oxides on the surface of the metal (firescale) or combining with copper deeper within the metal, creating cuprous oxides (firestain)



Related to this question, because they all are applied the same way. Has anyone seen a difference between boric acid & alcohol, Firescoff Ceramic Flux and Cupronil Anti-Firescale/Flux Coating in relation to fire scale prevention on sterling silver? Is one better than the other? I’ve used them all and can’t tell a difference between them.

This also might be good info for EmilyM85765 to know.




Ok thanks.

This is helpful

Ganoksin could have a “science department that did experiments like this. It would be valuable

I bought a small bottle of firescoff a while back to try, but i didn’t like how it needed to be applied by spraying and then heating, so I just went back to the standard and the small bottle is still full. Honestly, I switched to Argentium so I wouldn’t have to use a barrier flux because I hate the smell of it. I also like all of the other beneficial qualities that Argentium comes with.



I have only used the homemade Prips Flux version of these fluxes, which I have heard compares similarly, for a lower cost…I have found it to be an exceptionally good barrier flux!..used properly, the resulting metal remains beautifully silver and free of firescale/ stain.

…the only challenge is to spray it on to the piece at the proper heated temperature to achieve an instantaneous and frosted/ powdered full coverage…I continue to experiment to find the “perfect” spray bottle that will not fail after short use…I am now wondering if the above mentioned proprietary brands have superior spray bottles…?

I am recalling a past post by Peter Rowe, (which I can never find when i need it!..)

If I recall correctly, (correct me it i get this mixed up) he mentioned that Boric Acid alone has a shorter working time and temperature range (ie: Boric Acid and denatured alcohol)…and that combining it with Borax (versus just using a Borax cone and dish) increases the temperature range and working time of the combination, making it active earlier and longer…and that the TSP is a wetting agent and that adding it to the combination increases viscosity and surface tension of the mixture (ie: better coverage…it is used as a cleaner for walls before painting…so…perhaps a soap? saponic?).

basically, when metal that is a copper alloy is heated, the oxygen in the atmosphere as well as the oxygen in the fuel/gas mixture can combine with the copper in the alloy, to create cupric oxides (firescale on the surface) as well as cuprous oxides (firestain within the metal)…especially because Sterling Silver has the ability to absorb a lot of oxygen…

so, i think the goal of the flux is to provide full coverage (thus the TSP or any ingredient that lowers surface tension), and to create an oxygen barrier, that can absorb oxygen any copper oxides before they combine with the oxygen on/ in the metal), and which starts working early on (lower temperature-wise), and for as long as possible (staying active longer), while oxygen is present in the heat…(I read somewhere that the Boric Acid alone has a higher melting point, that is lowered when mixed with borax…?)

…so, I am guessing that the proprietary brands of flux have ingredients based on achieving these and related goals…?



I think I use a method similar to Rob’s most of the time. Boric acid and denatured alcohol. But I have used a method described in a manual whereby the metal is heated to a straw color and then the work is dipped in a mixture of boric acid in suspension with distilled water. The work piece is pulled out and set to dry before soldering with Battern’s or Boric Acid and Alcohol takes place. I will endeavor to find that manual and quote it directly however playing in an Irish band in March leaves me little time for anything else.

Don Meixner


By TSP, I’m assuming that you are refering to trisodium phosphate. It IS used to clean walls before painting, and to remove and kill mold. It’s a highly effective cleaner but is not available at most retail outlets for cleaners (e.g grocery or hardware stores) as phosphates have been banned in household cleaners. I bought some to clean mold off the wall paper in the bathroom…TSP acts like a detergent and does lower surface tension, as all detergents do. So far as fire scale prevention and fluxing is concerned, the best results can be had by pickling and cleaning, reapplying the scale preventer frequently. Cleaning metals often and keeping them clean keeps oxidation and firescale down.

Good luck with playing in an Irish band… Happy St. Patrick’s day!

1 Like

I was able to buy real TSP via Amazon several years ago…Rob

I bought a box of it from a local chemical supplier years ago… still have half a box left over from cleaning mold on the wall… don’t need very much at all for it to be effective. It does kill black mold, in addition to being used as an ingredient in firescale prevention flux.

Im glad someone else cant tell a difference. I have so many kinds its ridiculous. I see a new one someones using, buy it thinking I’m missing something, and theres no difference at all. Lol.